The present invention relates to medical instruments utilized in securing marrow tissue samples from bone structures.
A biopsy medical instrument is an instrument which is designed to take samples of tissue. Typically, a biopsy device that is utilized to obtain samples from bone consists of a hollow cannula that is surrounding a stylet. The stylet includes a sharp distal tip which extends outwardly from the cannula when the stylet is secured inside the cannula. The combined cannula and stylet is used to penetrate through the outer layer of the bone, called the cortex, which is considerably harder than the trabecular bone layer and the tissue within the bone that is sampled, referred to as the marrow. Once the stylet is removed and the cannula is extended further into the medular cavity, thereby capturing marrow tissue for a sample.
The architecture of the tissue sample that is removed by the biopsy device is critical in several respects. Initially, the size of the sample is important, with larger tissue sample sizes representing better samples for subsequent testing to be performed on the tissue. However, the larger the cannula and stylet that are inserted into the bone, the more pain is generated at the site of the penetration for the patient. In addition, it is important that the sample be taken without damaging the marrow tissue. However, in removing the tissue sample the tissue must be excised from the remaining tissue. This removal can result in compromising the tissue sample by damaging the tissue sample.
Several approaches have been taken to secure large, undamaged tissue samples using bone marrow biopsy devices. However, each of these approaches has significant drawbacks which limit commercial and clinical usefulness. For example, one such approach utilized suction provided at the proximal end of the cannula. The suction is designed to pull the tissue sample into the cannula and retain the tissue sample inside the cannula. While in theory such suction would help secure larger tissue samples, in practice exposure to such suction forces results in damage to the marrow tissue when the sample is removed from the patient.
Another approach utilizes a snare in the form of a coil at the distal end of the cannula. When rotated, the coil decreases in diameter to secure the biopsy tissue sample in the cannula. Examples of such devices are disclosed in Goldenberg et al. U.S. Pat. No. 5,522,398 and Goldenberg et al. U.S. Pat. No. 5,634,473. While again in theory such a device would help secure larger tissue samples, in practice it subjects the tissue sample to compression forces which causes damage to the sample.
Other approaches include the use of inwardly projecting members such as scallops within the cannula. Such devices are disclosed in Rubinstein et al. U.S. Pat. No. 5,462,062 and Rubinstein et al. U.S. Pat. No. 5,885,226. The theory behind such devices is that when the tissue sample is inserted into the cannula, the inward direction of the scallops allows the tissue sample to slide over such projecting members but when the tissue sample is removed from the patient the projecting members latch onto the tissue sample to secure the tissue sample in the cannula. Again, however, this theory fails in practice as it causes trauma to the tissue when the tissue sample is removed from the patient.
Other approaches include providing apertures on the side of the cannula which, in theory, allow tissue to expand into such apertures to help secure the tissue sample in the cannula. Likewise, one approach, such as that disclosed in Goldenberg U.S. Pat. No. 5,843,001, utilizes a screw member in the cannula which is designed to urge the tissue inwardly and retain the in the cannula. Once again, providing a cavity for the tissue sample that is not smooth results in damage to the tissue when the tissue sample is removed from the patient.
Yet another approach at securing the biopsy sample within the cannula involves the use of a pair of coaxial cannulas, such as that disclosed in Rubinstein et al. U.S. Pat. No. 5,595,186. One of the two cannulas includes a curved section that acts as a cam to compress the inner cannula around the tissue sample when the inner cannula is withdrawn from the outer cannula. Once again, in theory this would help to secure the tissue within the cannula, but in practice it subjects the tissue sample to such compression forces that damage to the sample is caused. In addition, the use of dual cannulas acts to either decrease the size of the tissue sample or to increase the size of the biopsy device causing increased pain to the patient. A similar approach disclosed by Swaim U.S. Pat. No. 5,807,277 utilizes an additional coaxial hollow cannula designed to sheer or cut-off the tissue when the two cannulas are rotated relative to each other. However, because such devices require additional hardware in the cannula, either the size of the tissue sample is decreased or the size of the biopsy device is increased.
Mittermeier et al. published International Patent Application No. WO 00/10454 discloses a bone biopsy device comprising an outer cannula and inner cannula, wherein the distal end of the inner cannula contains a resilient deformable wall which constricts during the sampling. One drawback of this design is that the interruptions in the tissue receiving portion of the inner cannula facilitate wall deformation thereof, but also compress the obtained sample while compromising the structural integrity of the receiving portion of the inner cannula in operation.
Difficulty has been encountered in the art in the balancing between the structural properties of bone biopsy devices and desired sampling attributes. The ability for bone biopsy devices to sample in a consistent manner without unnecessary damaging forces exerted upon the sample taken has especially proven challenging. In addition to these problems, accommodating patient comfort by reducing the need for multiple site sampling is another challenge.
There exists a need in the art for bone biopsy devices that have improved operative designs and characteristics. What would be desirable is a bone marrow biopsy device that is able to consistently secure a large tissue sample while avoiding increasing the size of the biopsy device thereby minimizing the pain experienced by the patient during the procedure. Also desirable would be a device that avoids subjecting the tissue sample to undue forces, whether such forces be compression, suction, etc. Reducing trauma to the patient from multiple sampling would also be desirable.
The present invention is able to secure a large tissue sample while avoiding increasing the size of the biopsy device thereby minimizing the pain experienced by the patient during such procedure. The present invention further avoids subjecting the tissue sample to undue forces, whether such forces be compression, suction, etc., thus reducing damage to the tissue following removal of the sample from the patient. Yet another advantage of the invention is that multiple samples can be obtained from a single penetration episode into the bone, thereby reducing the trauma of the biopsy procedure to the patient and increasing patient comfort.
The present invention provides a bone marrow biopsy device that includes a handle, an outer cannula, a stylet, and an inner member. The outer cannula is secured in the handle. The outer cannula defines a distal tip that is tapered to provide a distal cutting edge. The stylet is designed to be inserted in the outer cannula. The stylet defines a sharp distal tip. The inner member is designed to be inserted in the outer cannula. The inner member defines a cutting finger and has a tip which is beveled. When the inner member and outer cannula are assembled, the distal tip of the cutting finger of the inner member terminates at a position proximal to the distal tip of the outer cannula.
Thus, there is disclosed a bone marrow biopsy device comprising a handle; an outer cannula secured in the handle, the outer cannula defining a distal tip that provides a distal cutting edge; a stylet designed to be inserted in the outer cannula, the stylet defining a sharp distal tip; and an inner member designed to be inserted in the outer cannula, the inner member defining a cutting finger.
Thus, there is further disclosed a member for use with a bone marrow biopsy device comprising a proximal end formed with a hub that secures the member; and a distal end that defines a cutting finger.
In a preferred embodiment, the inner member further comprises markings on the surface of the proximal portion thereof to indicate the length of the sample to be obtained relative to the outer cannula. In another preferred embodiment, the cutting finger has a width designed such that the cutting finger is wide enough to maintain the structural integrity of the cutting finger while being sufficiently narrow to avoid subjecting a tissue sample to compression forces. In one embodiment, the width of the cutting finger is from about 60% to about 75% of the circumference of the inner member. In a further preferred embodiment, the cutting finger of the inner member has a length of up to about 4.0 cm.
There is further disclosed a kit for use in obtaining a bone marrow biopsy comprising a handle having an outer cannula secured therein, the outer cannula defining a distal tip that provides a distal cutting edge; a stylet designed to be inserted in the outer cannula, the stylet defining a sharp distal tip; and an inner member designed to be inserted in the outer cannula, the inner member defining a cutting finger.
There is disclosed a method for sampling bone marrow tissue comprising: inserting a stylet into an outer cannula; penetrating the bone cortex with the stylet and the outer cannula; removing the stylet; further inserting the outer cannula into a medular cavity, thereby trapping bone marrow tissue within the outer cannula; extending an inner member into the outer cannula, the inner cannula defining a cutting finger; rotating the inner member to shear off the specimen with the cutting finger; and removing the specimen from the patient.